import java.util.Scanner;       
public class Sex {
  public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
         int[] grade = new int[5];         
         for(int i=0; i<grade.length; i++){    
               grade[i] = in.nextInt();
          }       
         RR rr = new RT(grade);
         double dd = rr.mark();
         System.out.printf("%.2f",dd);
	}
}
abstract class RR{       
   int[] grade;
   public RR(int[] grade){
      this.grade = grade;
   }
   public abstract double mark();
}
class RT extends RR{     
	public RT(int[] grade) {
		super(grade);        //继承父类有参构造函数
	}
	public double mark(){
		double x = (grade[1]+grade[2]+grade[3])/3;     //平均值
		return x;
	}
}
